1. Field of the Invention
The present invention relates to injection laser diodes and, more particularly, to such diodes with resonance damping means.
2. Description of the Prior Art
There are many applications for injection laser diodes, including applications requiring modulation at high frequencies. As is appreciated by those familiar with the art, an injection laser diode, hereafter simply referred to as the laser diode, experiences resonance. It is this resonance which sets the upper limit on the useful frequency range within which the laser diode can be modulated, without experiencing resonance. This aspect is discussed in the prior art literature, e.g., in "Semiconductors Lasers and Heterounction Leds", by Kressel et al., Academic Press, New York, 1977. Briefly, as is appreciated, the resonance peak can be reduced, i.e., the resonance dampened, by reducing the effective lifetime of the carriers in the active region of the laser diode.
Various arrangements have been suggested to achieve such reduction. These arrangements include connecting an electrical network in parallel with the laser diode, utilizing the mechanism of carrier diffusion out of the active region, or with the addition of another laser to direct light to the active region. Some of these arrangements are suggested in the following prior art references:
T. Hong and Y. Suematsu, "Suppression of Resonance-Like Phenomena in the Light Output of Directly Modulated Injection Lasers by .pi.-Type Suppressor Circuit," The Trans. IECE Japan, E61, pp. 121-124 (1978).
Y. Suematsu and T. Hong, "Suppression of Relaxation Oscillation in Light Output of Injection Lasers by Electrical Resonance Circuit," IEEE J. Quant. Electron. QE-13, pp. 756-762 (1977).
K. Furuya, K. Suematsu, and T. Hong, "Reduction of Resonance-like Peak in Direct Modulation Due to Carrier Diffusion in Injection Laser," Applied Optics 17, pp. 1949-1952 (1978).
N. Chinone, K. Aiki, M. Nakamura, and R. Ito, "Effects of Lateral Mode and Carrier Density Profile on Dynamic Behaviors of Semiconductor Lasers," IEEE J. Quant, Electron. QE-14, pp. 625-631 (1978).
D. Wilt, K. Y. Lau and A. Yariv, "The Effect of Lateral Carrier Diffusion on the Modulation Response of a Semiconductor Laser," J. Appl. Phy., 52, pp. 4970-4974 (1981).
All of these arrangements, except for the carrier diffusion, suffer from one very basic disadvantage, namely the need for extensive networks, such as a multicomponent circuit, e.g., an RLC or Pi-shaped network or an additional laser, all of which are external to the laser diode. Whereas, a laser diode, by itself, is extremely small, which is highly desirable, the need to attach a much larger network to it, greatly increases the overall size of the resonance-damped laser diode. This increase in size is highly undesirable, and often unacceptable. As to the use of carrier diffusion to dampen the laser diode's resonance, it results in reduced laser efficiency at all frequencies, including those below resonance. Such efficiency loss is clearly undesirable. A need therefore exists for a new arrangement to dampen the resonance of a laser diode. Alternately stated, a need exists for an arrangement to dampen the resonance of a laser diode, without appreciably increasing its actual size, or without considerably affecting its efficiency.